TPEs are block co-polymers made of a hard component and a soft component. The two components undergo microphase separation. The solid domains formed by the hard component are glassy or crystalline. The solid domains are dispersed within a matrix of the soft component and act as both physical crosslinkers and filler particles. The polymer chains of the soft component have a Tg below the service temperature and are able to stretch but are restricted from flowing. In the absence of the hard component, the soft component can flow.
TPEs made from copolymers of polyisobutylene (PIB) are well known in the art. See e.g. U.S. Pat. Nos. RE 34,640, 5,633,234, U.S. Pat. Nos. 4,946,899, 5,428,111, 5,458,796, 5,721,331 4,910,261, 6,747,098, and 5,081,179, the disclosures of which are incorporated herein by reference in their entirety. The great advantages of many recent TPE PIB networks over prior PIB networks, such as the well-known general purpose Butyl Rubber, are that (a) they can be made by “liquid rubber” technology (i.e., by mixing two relatively low molecular weight viscous liquid prepolymers in a mold to give a crosslinked rubber), and (b) they can be recycled upon heating (“green liquid rubbers”). Butyl rubber networks, by contrast, are made by first laboriously mixing the high molecular weight uncured rubber with sulfur and various harsh curatives on large steel blenders/mills that require huge amounts of energy to operate; and then crosslinking (“curing”) the blend to permanent networks by again heating to high temperatures and pressures. Thus, butyl rubber is a thermoset, i.e., it cannot be recycled. In contrast, TPE can be recycled, and can be prepared by liquid processing technologies, which are far simpler and consume far less energy than conventional methods